GB2517171A - Power Supply - Google Patents

Power Supply Download PDF

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Publication number
GB2517171A
GB2517171A GB201314493A GB201314493A GB2517171A GB 2517171 A GB2517171 A GB 2517171A GB 201314493 A GB201314493 A GB 201314493A GB 201314493 A GB201314493 A GB 201314493A GB 2517171 A GB2517171 A GB 2517171A
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Patent type
Prior art keywords
power supply
terminal
current
load
power
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
GB201314493A
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GB201314493D0 (en )
Inventor
Jerry Lister
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
HARVARD ENGINEERING PLC
Original Assignee
HARVARD ENGINEERING PLC
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Classifications

    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/06Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode
    • H02M7/062Avoiding or suppressing excessive transient voltages or currents
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M1/32Means for protecting converters other than automatic disconnection
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
    • H02M5/04Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
    • H02M5/06Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using impedances
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B33/00Electroluminescent light sources
    • H05B33/02Details
    • H05B33/08Circuit arrangements not adapted to a particular application
    • H05B33/0803Circuit arrangements not adapted to a particular application for light emitting diodes [LEDs] comprising only inorganic semiconductor materials
    • H05B33/0806Structural details of the circuit
    • H05B33/0809Structural details of the circuit in the conversion stage
    • H05B33/0815Structural details of the circuit in the conversion stage with a controlled switching regulator
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B41/00Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14Circuit arrangements
    • H05B41/36Controlling
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M2001/0003Details of control, feedback and regulation circuits
    • H02M2001/0009Devices and circuits for detecting current in a converter
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02BCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B20/00Energy efficient lighting technologies
    • Y02B20/30Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
    • Y02B20/34Inorganic LEDs
    • Y02B20/341Specially adapted circuits
    • Y02B20/346Switching regulators
    • Y02B20/347Switching regulators configured as a current source

Abstract

A power supply 100 and corresponding method controls the supply of power from a power source 120 such as a mains supply to a load 130. It has an input terminal 1001, 1002 for connecting to a power source 120, an output terminal 1003, 1004 for connecting to a load 130, and current monitoring means (such as a voltmeter across an inductor) that monitor the rate of change of the current flowing in the power supply 100. The power supply 100 generates a control signal according to the rate of change of current detected by the current sensor. A current controller 160 controls the current flowing from the power supply 100 to the load 130 (for example, by means of a transistor) according to the control signal. The power supply may reduce peak currents in phase controlled (e.g. TRIAC) mains supply systems.

Description

Power Supply [0001] The present invention relates to power supplies for controlling the supply of power from a power source to a load, and to apparatus comprising such power supplies. Certain embodiments relate to power supplies for controlling the supply of power from power sources such as phase-controlled mains supplies.

BACKGROUND

[0002] When driving electronic power supplies from a phase (for example, TRIAC) controlled mains supply there can be a serious problem with high peak currents giving rise to acoustic noise and the risk of (TRIAC) de-latching.

[0003] Existing methods to limit these peak currents include the use of resistance or inductance in series with the mains supply, or a switched resistor method.

[0004] If resistance is used! it may also have a bypass filter to limit power loss. This has the effect of making the method only suitable for low power products. Therefore this method is not optimal for all operating conditions and can result in wasted power.

Additionally, using resistance does not limit peak current well which can cause a high level of electrical stress in the system. Finally, the rate of change of current is not controlled which can lead to a buzzing problem (or electrical noise) in the circuit.

[0005] Using series inductance gives lower losses compared to using resistance, but the component needs to be relatively large to be effective. The large value inductors required are relatively expensive, providing a disadvantage for this method. Also, the circuit may require damping to limit current ringing where there is an unwanted oscillation of the current. Saturation of the inductor itself means the rate of current change may not be well controlled, and power loss in the inductor can also be high due to resistance. As in the previous method, efficiency is poor when series inductance is used in a circuit without a dimmer, and there results in high electrical stress through poorly controlled peak currents.

[0006] The switched resistor method is not as efficient as the others, and also has the risk of TRIAC de-latching. This latter problem is a result of high peak currents and ringing due to the digital control of an FET used for the switching. In addition to de-latching, these factors can result in electrical stress on the components involved. Unlike the other two methods the use of switched resistors allows for higher power products. However, the efficiency may be compromised due in part to the power loss in the resistor being high.

Finally, as in the other methods the rate of change of the current is not controlled, which may lead to the same buzzing problem.

[0007] It is an object of certain embodiments of the present invention to solve, at least paitly, at least one of the above-identified problems.

BRIEF SUMMARY OF THE DISCLOSURE

[0008] According to a first aspect of the present invention there is provided a power supply for controlling the supply of power from a power source to a load, the power supply comprising: at least one input terminal (and in certain embodiments two input terminals) for connecting to a power soulce; at least one output terminal (and in ceitain embodiments two output terminals) for connecting to a load; current monitoring means arranged to monitor a rate of change of a current flowing in the power supply, the current at least partly determining a current flowing in a load connected to the output terminal, and generate a control signal indicative of the rate of change; and current control means arranged to receive the control signal and control the current flowing in the power supply according to the control signal.

[0009] An advantage of certain embodiments of the first aspect of the present invention is that the rate of change of the current is monitored and the current actively controlled in response, enabling lower peak currents to be achieved.

[0010] Another advantage of ceitain embodiments of the first aspect of the present invention is the reduction of electrical stress due to the lowering of peak currents in the power supply and /orthe load.

[0011] Another advantage of certain embodiments of the present invention is that they can allow for more electrical products to be connected to a mains contact breakei. This is because contact bieakers aie rated for continuous current and surge cuirent, and ceitain embodiments of the present invention reduce surge current when compared to other designs. This reduction in surge current may be by at least a factor of 3. The result of this is a reduction in the cost of installation and / or a reduction in the risk of the mains contact bieaker (nuisance) tripping.

[0012] In certain embodiments, the current monitoring means may comprise an inductor, the inductoi being arranged to cariy said cuirent flowing in the power supply, which determines, at least in part, the current flowing in the load. The monitored current thus corresponds to the current being driven through the load by the power source. The monitored cuirent in certain embodiments is the load curient, but in alternative embodiments the monitored current corresponds to the load current, but is not identical to it.

[0013] In certain embodiments, the control signal is a voltage developed across the inductor.

[0014] In certain embodiments, the current control means comprises a controllable device, which may also be described as a switching device, airanged to cairy the current flowing in the power supply. In certain embodiments the controllable device comprises a control terminal, and second and third terminals, and the device is arranged such that said current flows from the second to the third terminal. A control signal (e.g. a control voltage, oi control cuirent) is applied to the control terminal to control the conductivity of the cuirent path from second to thud terminal, and hence the control signal can be used to control said current. The controllable device in certain embodiments is thus a device having a controllable conductivity. In certain embodiments the controllable device is a transistor, which can also be described in this context as a switching device. In certain embodiments, such switching devices may be operated predominantly, or solely, in a generally linear mode, that is, during normal operation, they are in a permanently conducting state, with the magnitude of their conductivity (from collector to emitter, or source to drain) being modulated by the control signal applied to their base or gate.

[0015] In certain embodiments, the controllable device is arranged in series with the inductor.

[0016] In certain embodiments, the controllable device is a transistor, for example one of: a field effect transistor, FET; an insulated-gate bipolar transistor, IGBT; or a bipolar junction transistor, BJT.

[0017] In certain embodiments, the current control means further comprises a circuit airanged to control a voltage applied to a control terminal (e.g. a gate terminal oi similai) of the controllable device accoiding to said control signal.

[0018] In certain embodiments, the circuit complises a second controllable device (e.g. a second transistor, such as a BJT, FET or IGBT) having a control terminal connected to a first terminal of the inductor, a second terminal (e.g. an emitter terminal or similar) connected to a second terminal of the inductor, and third terminal (e.g. a collector terminal oi similar) connected to the contiol terminal of the first controllable device.

[0019] In certain embodiments, the power supply further comprises a resistor arranged in series with the inductoi such that the resistor also carries said cuirent flowing in the powei supply.

[0020] According to another aspect of the invention there is provided a method for controlling a supply of power from a power source to a load, the method comprising: monitoring a rate of change of one of an electrical current driven through the load by the power source and an electrical current corresponding to the electrical current driven through the load by the power source; generating a control signal indicative of said rate of change; and controlling the electrical current driven through the load by the power source according to the control signal.

[0021] In certain embodiments, monitoring the rate of change of the electrical current and generating the control signal comprises passing the monitored electrical current through an inductor such that a voltage is developed across the inductor.

[0022] In certain embodiments, the control signal is the voltage developed across the inductor.

[0023] In certain embodiments, controlling the electrical current comprises controlling a conductivity of a device arranged to carry at least a portion of the electrical current driven through the load by the power source.

[0024] In certain embodiments, the device is connected in series with the inductor.

[0025] In certain embodiments, the device is a first transistor, for example: a field effect transistor, FET; an insulated-gate bipolar transistor, IGBT; or a bipolar junction transistor, BJT.

[0026] In certain embodiments, controlling the electrical current further comprises controlling a voltage applied to a control terminal of the first transistor.

[0027] In certain embodiments, controlling the voltage applied to the control terminal of the first transistor comprises providing said voltage with a control circuit comprising a second transistor.

[0028] Another aspect of the invention provides power supply apparatus for supplying power to a load, the apparatus comprising a power supply in accordance with the above-mentioned first aspect, and a power source connected to the at least one input terminal.

Examples of such power supply apparatus include, but are not limited to: domestic, commercial and industrial lighting including office lighting, downlights, flat panel lighting, retail shop lighting, outdoor lighting, street lighting, signage lighting (for example, stationary road traffic lighting), and as a traffic lights LED driver.

[0029] Another aspect provides apparatus comprising a power supply in accordance with the first aspect, and a load connected to the at least one output terminal. Examples of such apparatus include, but are not limited to: industrial power supplies for computer and telecom applications, personal computer power supplies, power supplies in consumer audio visual equipment, industrial and domestic battery chargers, traffic light power supplies and triac controlled devices such as motor speed control and cooling fans.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the present invention are further described hereinafter with reference to the accompanying drawings, in which: [0031] Fig. 1 is a schematic representation of a system embodying the invention and supplying power from a mains power source to a load using a power supply also embodying the present invention; [0032] Fig. 2 is a circuit diagram of a power supply embodying the present invention; [0033] Fig. 3 is a circuit diagram of a power supply embodying the present invention where additional components are included to provide various functions; [0034] Fig. 4 is a schematic representation of apparatus in accordance with the prior art; [0035] Fig. 5 is a schematic representation of other apparatus in accordance with the prior alt; [0036] Fig. 6 is a schematic representation of another apparatus in accordance with the prior ad.

DETAILED DESCRIPTION

[0037] In the following it will be appreciated that the presented circuits and schematics are not presented in absolute detail. As a skilled person would understand, such circuits may often include many additional components -such as resistors, capacitors or diodes -to aid in the functionality of the circuit as a whole. These additional components may function to safeguard against adverse effects which may otherwise be induced in the circuit (such as component damage when surge testing) or to mitigate problematic behaviour inherent in other components when used in such circuits. The mitigation of adverse electronic effects is well known, and it should be understood that the embodiments of the present invention presented herein can be readily adapted to mitigate these problems while still relating to the present invention.

[0038] It will be appreciated that the term "power-supply" is well understood in the present field, and encompasses, for example but not limited to, apparatus which may also be described as: "ballast", "electronic transformer", "control gear", "electronic control gear", "PSU", "SMPS", "inverter", "drivers", "LED drivers", "charger" and "battery charger".

[0039] Fig. 1 is a schematic representation of a system embodying the invention and supplying power from a mains power source to a load, using a power supply 100 which also embodies the present invention. The system comprises a power supply 100, a mains supply 120 as a power source, a load 130 and a dimmer 140. The power supply 100 comprises two input terminals 1001, 1002 for connecting (and, in the figure, connected) to the power source, and two output terminals 1003, 1004 for connecting (and, in the figure, connected) to the load 130. The power supply 100 in this particular embodiment also comprises an EMC filter 150, a power conversion stage 160, and a power supply unit 110, which may also be described as a power supply sub-unit, sub-assembly, or sub-circuit, as it forms pad of the power supply 100 as a whole. The power supply unit 110 also embodies the present invention. The power supply 100 additionally comprises rectifying means 1005 comprising an arrangement of four a diodes. The EMC filter comprises capacitors 152 and 154.

[0040] The mains supply 120 provides a source of alternating current to the system, and includes a live terminal 122 and a neutral terminal 124. The live terminal 122 is connected to the dimmer module 140, which in turn is connected to terminal 1002. Thus, the mains power supply 120 is connected to the input terminals 1001, 1002, via the dimmer module, and provides an alternating voltage across those input terminals. Components of the power supply unit 110 are shown in figure 2, and the three terminals 111, 113, and 115 of that unit 110 are labelled A, B, and C respectively to clearly show how they are connected in the power supply 100 of fig. 1. Generally, in operation of the system of figs. 1 and 2, application of an alternating drive voltage across input terminals 1001, 1002 results in a uni-directional current being driven through the load, as a result of the rectifying action of the rectifying means 1005. This current is in the forward direction through diode 102, and returns, from the load to the power source, through the power supply unit 110, flowing from terminal C to terminal B. The current flowing through the control unit 110 from terminal C to B thus corresponds to the load current being driven by the power source (although it will be appreciated that there may be a small difference between that current from C to B and the load current, as a consequence of any small currents in EMC filter capacitors 152 and 154. Although the embodiment of fig. 1 incorporates a dimmer module 140, it will be appreciated that in certain alternative embodiments of the present invention, no dimmer is present in the system, and instead the power supply 100 receives power directly from the mains supply 120 (i.e. is directly connected to it). In certain embodiments incorporating a dimmer, the dimmer may comprise a triac, but other dimmers may be utilised in alternative embodiments.

[0041] Referring again to fig.2, it will be appreciated that the current path from terminal C to B in this example comprises a resistor R4 in parallel with a series arrangement of inductor Li and the conductive channel of transistor 02. In certain alternative embodiments, resistor R4 may be omitted. When transistor 02 is in a conducting state, the current path through 02 and Li in series may have much lower resistance than R4, and so the majority of current flowing from C to B will flow through Li. It will be appreciated that the current flowing through Li corresponds to the current flowing in the load. The details of the correspondence between Li current and load current depend, of course, on the magnitude of R4. It will also be appreciated that controlling the current through Li has the effect of controlling the current flowing in the load. Thus, the current flowing through 02, which is the same as the current flowing through Li, at least partly determines the load current. Li thus provides means for monitoring a rate of change of the current 10 flowing through transistor 02 (or other controllable device, in alternative embodiments), because a voltage is developed acioss Li, the magnitude of that voltage being proportional to dlQ/dt. That voltage is supplied, via resistor R3, the control terminal (the base terminal in this example) of a second transistor 01, which has a second terminal connected to the gate terminal of 02 and a third terminal connected to terminal B. This control voltage controls the current flowing through 01 (which also flows from terminal A, through Dl, Ri, and R2, and so determines the voltage applied to the gate of 02.

Generally, the higher the rate of change of 10, the higher the voltage applied to the base of Qi, the higher the current through Di, and hence the lower the voltage applied to the gate of 02, which in the arrangement of figs 1 and 2 acts to reduce the conductivity of the channel in 02 (from source to drain). This increases the resistance of the current path through 02, and so reduces 10. Control of 10 is thus achieved, according to the detected rat of change of ID, so controlling load current.

[0042] Thus, in the embodiment illustrated by figures i and 2, the power supply unit 110 further comprises: an inductor 2i 0, Li arranged to monitor a current (10) flowing in the power supply 100, and at least partly determining load current, as current monitoring means, the inductor being arranged to produce a control signal; a first device with controllable conductivity, in the form of a field effect transistor (FET) 220, arranged to control the current being monitored (ID); and a second device with controllable conductivity, in the form of a bipolar junction transistor (BJT) 230, arranged to supply a control signal to the FET 220 according to the rate of change of the monitored current. The first and second controllable devices thus together provide current control means. In certain alternative embodiments, the FET 220 may be replaced by another suitable switching device such as a BJT, an insulated-gate bipolai transistoi (IGBT), or another device, such as a linear switching device. Here, a linear switching device is used to denote a switching device which allows for a range of conductivity states and is not confined to either an ON' 01 OFF' state only. Similaily, in ceitain embodiments the BJT 230 may be ieplaced by an FET, IGBT or another suitable linear switching device.

[0043] The power supply unit 110 in the present embodiment further comprises a zener diode Z1,240, a diode Dl, 250, a first resistor Ri, 260, a second iesistoi R2,270, and a third resistor 280. The diode 250 is connected in series between the terminal A, 111 and the first resistor 260, wherein the anode terminal of the diode 250 is connected to the terminal 111 and the cathode terminal of the diode 250 is connected to the first resistor 260. The zenei diode 240 is connected between a node 201 (between the first and second resistors) and a rail 203 connected to terminal 113. The zener diode 240 is arranged such that the cathode terminal of the zener diode 240 is connected to the first resistor 260, and the anode terminal of the zener diode 240 is connected to the iail 203. It will be appieciated that the zener diode 240 protects against surges, allowing curient to flow directly from terminal A, 110 to terminal B, 113 under certain conditions. The voltage at the low side of the second resistor 270 controls the conductivity of the FET 220. One of the source and diain terminals ot the FET 220 is connected to the terminal 115, while the other one of the source and drain terminals of the FET 220 is connected to a first terminal of the inductor 210. A second terminal of the inductor 210 is connected to the rail 203. The operation of ceitain power supply systems embodying the invention will now be described in further detail. When a triac dimmer turns on, a high current tries to flow in 02, and EMC filter capacitors 152, 154. If no current reduction method were employed (i.e. without an embodiment of the invention) this could lead to several amps flowing in the mains and in the dimmer and power supplies. Howevei, in ceitain embodiments of the invention this problem is avoided or overcome, as follows. Initially, we shall consider an embodiment generally as shown in figs. 1 and 2, but not incorporating resistor R4. Initially, 02 is biased on and is low resistance. Current flows in Q2 and Li, and this causes a voltage to be developed across Li. The inductor 210 thus acts as a current monitor in the Power Supply 100, monitoring the rate of change of the cuirent. The voltage developed across the inductor 210 can be thought of as a control signal, which must be indicative of the rate of change of the current. This control signal is passed to the base terminal (it is provided as a base drive to 01) of the BJT 230, which begins to turn on. The action of 01 turning on causes Q2 to begin to tuin off (by loweiing the voltage at the gate of Qi. This action of 02 beginning to turn off (i.e. reducing its conductivity) reduces the current flowing in the inductor 210. This is a regulating action. It causes a constant voltage to appear across [1.

From the equation di!dt=V/L it can be seen that the rate of rise of current is controlled.

This condition continues until the EMC filter capacitors 152 and 154 are fully charged, but the di/dt limitation results in lower mains peak currents. In certain embodiments, a fourth resistor R4, 290 is connected between terminal C, 115 and rail 203. The fourth resistor 290 is designed to share power with the 02 (e.g. FET 220). It will be appreciated that the fourth resistor 290 is unnecessary if the thermal performance of the controllable device Q2 is within predetermined limits.

[0044] In certain embodiments, a fifth resistor may be placed in series with the inductor 210. The inductor 210 has resistance which acts to limit the peak current in the circuit. This limit can be adjusted through the addition of the fifth resistor.

[0045] In certain embodiments, the dimmer 140 may be a trailing edge dimmer, alternatively known as a transistor dimmer. Here, it is unlikely that the rate of change of the current will be high enough to activate the circuit, that is, to generate the control signal.

Therefore the FET 220 is permanently on, because of the initial bias. In this configuration, power loss in the system is greatly reduced.

[0046] In certain embodiments, the dimmer 140 is not present in the system. Here, the input terminals 1001 and 1002 are connected directly to the power source. This system functions in a similar manner to that described above when a trailing edge dimmer is present. The device Q2 (e.g. FET 220) remains permanently on and power loss is greatly reduced.

[0047] Fig. 3 is a circuit diagram showing another power supply unit embodying the invention and which may be incorporated in power supplies and apparatus also embodying the invention. It is similar to the embodiment shown in Fig. 2 but includes some additional components. It should be appreciated that these additional components are not co-dependent, and any of them can be added in isolation or in combination with any of the others unless stated otherwise in alternative embodiments.

[0048] The power supply unit 300 of Fig. 3 comprises terminals 111, 113, and 115, , a first rail 201, a second rail 203, an inductor 210, an FET 220, a BJT 230, a first zener diode 240, a first resistor 260, a second resistor 270, a third resistor 270 and a fourth resistor 290. These components are respectively arranged in the manner described as for Fig. 2.

[0049] The power supply 300 further comprises a first capacitor 310 connected between the cathode terminal of the first zener diode 240 and the second rail 203 between the terminal 113 and the anode terminal of the first zener diode 240. The first capacitor 310 stabilises the voltage on the first zener diode 240. In the absence of the first capacitor 310, the voltage could vary to such a degree that the circuit does not operate correctly.

[0050] The power supply unit 300 further comprises a second capacitor 320 connected across the collector and emitter terminals of the BJT 230 (01). The second capacitor 320 acts as a filter which adjusts the operating speed of the BJT 230. Additionally, the second capacitor 320 provides noise immunity against rapid changes in the current from the power source EMC filter 160. For example, the power source may be an alternating current main source.

[0051] The power supply unit 300 further comprises a third capacitor 330 connected across the emitter and base terminal of the BUT 230, wherein a first terminal of the third capacitor 330 connects to the emitter of the BJT 230 and a second terminal of the third capacitor connects to the base of the BUT 230. The third capacitor 330 provides a similar function to that of the second capacitor 320.

[0052] The power supply unit 300 further comprises a fourth capacitor 340 connected across the gate terminal of the FET 220 (02) and the drain terminal of the FET 220. The fourth capacitor 340 is arranged to act as a safeguard against high frequency oscillations in the FET 220.

[0053] The power supply unit 300 further comprises a fifth resistor 350 connected between the second rail 203 and the second terminal of the third capacitor 330. The fifth resistor 350 is arranged to form a voltage divider with the third resistor 280 to allow the adjustment of the turn on voltage of the BJT 230.

[0054] The power supply unit 300 further comprises a sixth resistor 360 connected from between the third resistor 280 and the first terminal of the inductor 210 to the second rail 203. The sixth resistor 360 is arranged to act as a damping resistor to reduce any voltage ringing in the inductor 210.

[0055] The power supply unit 300 further comprises a seventh resistor 370 connected between the second rail 203 and the second terminal of the inductor 210. The seventh resistor 370 is an adjustment resistor arranged to allow for the adjustment of the maximum current that can flow in the inductor 210, as described in an earlier paragraph with respect to Fig. 2.

[0056] The power supply unit 300 further comprises a second diode 380 connected across the sixth resistor 360. The second diode 380 is arranged such that the cathode terminal of the second diode 380 is connected between the sixth resistor 360 and both the first terminal of the inductor 210 and the third resistor 280, and the anode terminal of the second diode 380 is connected to the second rail 203 between the fifth resistor 350 and the sixth resistor 360. The second diode 380 is a reset diode arranged to clamp peak voltages due to back electromotive force generated in the inductor 210.

[0057] The power supply unit 300 further comprises a second zener diode 390 (Z2) connected across the gate terminal of the FET 220 and the source terminal of the FET 220. The second zener diode 390 is further arranged such that the cathode terminal of the second zener diode 390 is connected between the second resistor 270 and the gate terminal of the FET 220, and the anode terminal of the second zener diode 390 is connected between the source terminal of the FET 220 and the first terminal of the inductor 210. The second zener diode is arranged to protect the FET 220 by preventing voltage transients damaging the FET 220, as could occur during mains surge testing.

[0058] It will be appreciated that the components consistent between Fig. 2 and Fig. 3 are still performing similar functions. The inductor 210 performs monitoring of the current and generates a control signal indicative of the rate of change of the current. The FET 220 and the BJT 230 comprise a means to control the current in the circuit based on the control signal.

[0059] It will also be appreciated that further capacitors, resistors, diodes or any other components may be included in the circuit. The inclusion of such extra components may be required depending on the intended use of the power supply 300.

[0060] Fig. 4 shows a schematic representation of a prior art attempt at a solution to the problem of high peak currents, wherein a resistor is utilized in the system. The system is essentially the same as that shown in Fig. 1, but not including the power supply unit 110.

The system comprises a power supply unit 400, a mains supply 120 as a power source, a load 130, and a dimmer 140.

[0061] The power supply unit 400 comprises a resistor 410, a EMC filter 150 and a power conversion stage 160. In this prior art system, it is the resistor 410 which provides the current control in the power supply unit 400.

[0062] The power supply unit 400 features excessive power loss and so is only suitable for low power products, such as those rates less than 10 Watts. Additionally, peak currents are not limited well and so there is a high amount of electrical stress. The resistor 410 also only limits the peak current itself and so di/dt is not actually controlled, leading to a possible buzzing problem. Buzzing may be caused by the dimmer 140 producing large fluctuations in the current in the circuit. However, for this system efficiency is poorest when it is used without a dimmer, and so buzzing might be necessary sacrifice [0063] Fig. 5 shows a schematic representation of another prior art attempt at a solution to the problem of high peak currents, wherein an inductor is utilized in the system. The system is essentially the same as that shown in Fig. 4, except the resistor 410 is replaced byan inductor 510.

[0064] For this power supply unit to effectively limit peak current, a large value inductor will tend to be required. As such this may prove to be a very expensive solution. Even allowing for such an inductor 510 the peak currents are not controlled well and so there may be a high level of electrical stress in the system. The rate of change of the current di/dt is also not well controlled due to saturation of the inductor 510, leading to a possible buzzing problem, and correspondingly if there is no dimmer 140 present in the system then efficiency is poor. Power loss due to the resistance of the inductor 510 can also be high meaning this system is only suitable for low power products, for example those rating less than 20 Watts.

[0065] Fig. 6 shows a schematic representation of another prior art attempt at a solution to the problem of high peak currents, wherein a switched resistor, that is, a resistor functioning with a switch, is utilized in the system. The system is essentially the same as that shown in Fig. 4, except the resistor 410 is removed from the system, and a resistor 610 and FET 615 are included at a different point in the power supply unit 600. The FET 615 is connected across the resistor 610 such that the conductive state of the FET 615 determines the current in the power supply unit 600. In systems such as this, various circuits may be used to drive the FET 615, but principally the driving force will be time-dependent. For example, such a circuit may be provided such that the system operates as follows. At the point when the triac in dimmer 140 turns on, the FET 615 is non-conducting (or off) and power is provided to the load via resistor 610. This serves to limit the peak current, but power loss in the resistor 610 is high whilst it is conducting power to the load.

Additionally, when the triac turns on a delayed drive circuit is started with a predetermined delay time, for example 500ps. After this delay time elapses, the delayed drive circuit provides a gate drive signal to the FET 615 which then begins to conduct (or turn on) and so short circuits the resistor 610 thereby providing power to the load with low power loss.

When the mains voltage falls to zero, the delayed drive circuit is reset, FET 615 stops conducting (is turned off), and the system waits for the next time the triac turns on.

[0066] In this system di/dt is still not controlled, resulting in possible buzzing problems especially as the efficiency is low if there is no dimmer 640. The digital turn on of the FET 615 can lead to high peak currents and ringing, which can cause increase electrical stress.

Power loss in the resistor can also be high, although less than in the power supply unit 400 shown in Fig. 4. Therefore this power supply unit 600 can be used for higher power products but there will still be a compromise in efficiency.

[0067] Throughout the description and claims of this specification, the words "comprise' and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0068] Features, integers, or characteristics described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0069] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims (23)

  1. CLAIMS1. A power supply for controlling the supply of power from a power source to a load, the power supply comprising: at least one input terminal for connecting to a power source; at least one output terminal for connecting to a load; current monitoring means arranged to monitor a rate of change of a current flowing in the power supply, said current at least partly determining a current flowing in a load connected to said at least one output terminal, and generate a control signal indicative of said rate of change; and current control means arranged to receive said control signal and control said current flowing in the power supply according to the control signal.
  2. 2. A power supply in accordance with claim 1, wherein said current monitoring means comprises an inductor arranged to carry said current flowing in the power supply.
  3. 3. A power supply in accordance with claim 2, wherein said control signal is a voltage developed across said inductor.
  4. 4. A power supply in accordance with any preceding claim, wherein said current control means comprises a controllable device arranged to carry said current flowing in the power supply.
  5. 5. A power supply in accordance with claim 4, as depending from claim 2 or claim 3, wherein said controllable device is arranged in series with said inductor.
  6. 6. A power supply in accordance with claim 4 or claim 5, wherein the controllable device is a device having a controllable conductivity.
  7. 7. A power supply in accordance with any one of claims 4 to 6, wherein said controllable device is a first transistor.
  8. 8. A power supply in accordance with claim 7, wherein said first transistor is one of: a field effect transistor, FET; an insulated-gate bipolar transistor, IGBT; and a bipolar junction transistor, BJT.
  9. 9. A power supply in accordance with claim 7 or claim 8, wherein the current control means further comprises a circuit arranged to control a voltage applied to a control terminal of the first transistor, for example to a gate terminal of the FET or IGBT or to a base terminal of the BJT, according to said control signal.
  10. 10. A power supply in accordance with claim 9, wherein said circuit comprises a second transistor (for example a BJT, FF1 or IGBT) having a control terminal (for example a gate terminal or base terminal) connected to a first terminal of the inductor, a second terminal connected to a second terminal of the inductor, and a third terminal connected to the control terminal of the first transistor.
  11. 11. A power supply in accordance with any one of claims 2 to 10, further comprising a resistor arranged in series with the inductor such that said resistor also carries said current flowing in the power supply.
  12. 12. A method for controlling a supply of power from a power source to a load, the method comprising: monitoring a rate of change of one of an electrical current driven through the load by the power source and an electrical current corresponding to the electrical current driven through the load by the power source; generating a control signal indicative of said rate of change; and controlling the electrical current driven through the load by the power source according to the control signal.
  13. 13. The method of claim 12, wherein monitoring the rate of change of the electrical current and generating the control signal comprises passing the monitored electrical current through an inductor such that a voltage is developed across the inductor
  14. 14. The method of claim 13, wherein the control signal is the voltage developed across the inductor.
  15. 15. A method in accordance with any of claims 11 to 14, wherein controlling the electrical current comprises controlling a conductivity of a device arranged to carry at least a portion of the electrical current driven through the load by the power source.
  16. 16. The method of claim 15, as depending from claim 13 or claim 14, wherein the device is connected in series with the inductor.
  17. 17. A method in accordance with claim 15 or claim 16, wherein the device is a first transistor, for example: a field effect transistor, FET; an insulated-gate bipolar transistor, IGBT; or a bipolar junction transistor, BJT.
  18. 18. The method of claim 17, wherein controlling the electrical current further comprises controlling a voltage applied to a control terminal of the first transistor.
  19. 19. The method of claim 18, wherein controlling the voltage applied to the control terminal of the first transistor comprises providing said voltage with a control circuit comprising a second transistor.
  20. 20. Power supply apparatus for supplying power to a load, the apparatus comprising a power supply in accordance with any one of claims 1 to 11, and a power source connected to the at least one input terminal.
  21. 21. Apparatus comprising a power supply in accordance with any one of claims 1 to 11, and a load connected to the at least one output terminal.
  22. 22. Apparatus in accordance with claim 21, further comprising a power source connected to the at least one input terminal, for supplying power to the load.
  23. 23. A power supply, a method for controlling a supply of power from a power source to a load, power supply apparatus, or apparatus comprising a power supply and a load, substantially as hereinbefore described with reference to figures 1-3 of the accompanying drawings.
GB201314493A 2013-08-13 2013-08-13 Power Supply Pending GB201314493D0 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1570926A (en) * 1976-03-01 1980-07-09 Gen Electric Circuit for starting and operating gas discharge lamp
US4346332A (en) * 1980-08-14 1982-08-24 General Electric Company Frequency shift inverter for variable power control
US5917289A (en) * 1997-02-04 1999-06-29 General Electric Company Lamp ballast with triggerless starting circuit
US5965985A (en) * 1996-09-06 1999-10-12 General Electric Company Dimmable ballast with complementary converter switches
US20030094907A1 (en) * 2001-09-19 2003-05-22 Nerone Louis R. Method of delaying and sequencing the starting of inverters that ballast lamps

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1570926A (en) * 1976-03-01 1980-07-09 Gen Electric Circuit for starting and operating gas discharge lamp
US4346332A (en) * 1980-08-14 1982-08-24 General Electric Company Frequency shift inverter for variable power control
US5965985A (en) * 1996-09-06 1999-10-12 General Electric Company Dimmable ballast with complementary converter switches
US5917289A (en) * 1997-02-04 1999-06-29 General Electric Company Lamp ballast with triggerless starting circuit
US20030094907A1 (en) * 2001-09-19 2003-05-22 Nerone Louis R. Method of delaying and sequencing the starting of inverters that ballast lamps

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